22 Replies Latest reply on Jun 25, 2012 12:02 PM by gretchen_21

    Weird and unwanted color gradient after Photomerge

    gretchen_21

      Hi all,

       

      I got an annoying problem with a weird color gradient that appears where it shouldn't. My context is, that I'm producing underwater photomosaics. I use Photomerge for merging, which works great for the often uniform seabed sediment images.

       

      [merge1.jpg]merge1.jpg

       

      The example is 65 images, btw. After placing the images manually within Photomerge, all looks great and ready for a perfect result after rendering (see above). However, when doing so, the final merge from within Photomerge (by clicking the OK button) creates perfect smooth blending, but a weird color gradient crossing the whole mosaic. this might originate in the fact, that the individual images also are not perfect, due to the uneven lighting situation underwater. In case all images are a bit reddish at the top and yellowish at the bottom, the final gradient over the full mosaic shows that as well. So to me it looks as if Photoshop just tries to be too smart and thinks, reapplying that pattern to the whole would be a great thing to do, which it isn't of course.

       

      [merge2.jpg]merge2.jpg

       

      I discussed this "bug" with (indeed very helpfull) Adobe staff and they recommended, to create the merge with the "Blend Images Together" option in the "Load" dialog unchecked. This creates a mult-layer document after rendering, with the images being placed properly but not blended.

       

      [merge3.jpg]merge3.jpg

       

      From here on, Adobe staff  recommended, I shall use the "Auto Blend Layers" function (File menu), but the result is identical as image 2. Ok, then, they recommended, to uncheck "Seemless Tones and Colors" in the "Auto Blend Layers" dialog. Indeed, this gets rid of the gradient, ...

       

      [merge4.jpg]merge4.jpg

       

      ... but shows very hard edges of the images, which get very prominent after optimizing levels:

       

      [merge5.jpg]merge5.jpg

       

      Was that understandable? Would anyone have experienced (and solved) the same issue? Or would anyone have an idea, how this could be handled in a way, that my resulting mosaic looks as perfect with respect to the original colors as in the initial merge window before rendering it (image 1)? Maybe it's a specific Color Setting (Edit menu)? I tried a lot so far but nothing helped and I might not have tried the right thing.

       

      The problem appears, btw, in CS3 to CS6!

       

      Any help appreciated, more information on request! Many thanks,

       

      g

        • 1. Re: Weird and unwanted color gradient after Photomerge
          Trevor.Dennis Adobe Community Professional (Moderator)

          Have you tried selecting the layers after Photomerge, and using Edit > Auto Blend layers (choosing seamless tones and colours)?

          • 2. Re: Weird and unwanted color gradient after Photomerge
            Berit Møller

            Try to merge a smaller amount of photos first and then go on by adding two or three photos more untill you have them all. I know it takes longer but you probably can get at better result. I always merge by hand and get super results because I prepare all photos and their edges before merging.

            • 3. Re: Weird and unwanted color gradient after Photomerge
              gretchen_21 Level 1

              @Trevor: Yes, the second picture shows the result of this. That's why I was told to uncheck it. Then, there is no gradient but hard edges (images 4+5). Thanks for your reply, g

              • 4. Re: Weird and unwanted color gradient after Photomerge
                gretchen_21 Level 1

                @Berit: That might be the way to go, I will try it. Just time is a factor sometimes and our mosaics usually consist of 3000+ images (largest one was 45,000), and since Photomerge/Photoshop can only render up to 150 or so (varies with resolution), the final mosaic consists of many many of those patches I showed here. But if this needs to be done step by step, I will do.

                 

                To your second point: In this example the images were not optimized before their use. This was kind of an exception. Normally, I run them all thru a batch job, with Match Color against a reference picture, which takes care of "harmonizing" levels and colors throughout the set, some Replace Color to get rid of the red & magenta, the dark corners turn into after level correction, and some extra lighting on the edges as well. The Lens Correction filter has some potential here (Vignette Removal). Thanks to our 50% overlap, the corners do not get visible much, but there's always some to see, of course. Are you doing underwater mosaics as well?

                 

                Thanks for your thoughts, g

                • 5. Re: Weird and unwanted color gradient after Photomerge
                  Berit Møller Level 1

                  @ gretchen

                  No I mostly do panoramas or I do stiching of paintings. I am a paintings conservator and I sometimes use 1:1 documentation photos which I stich togrether. Since It is documentation the details are realy, realy important. But I get dizy when thinking on the seize of your pictures. Are you familiar with the stiching app that National Gallery made? They made it especially for large pictures. I don't remember what it is called, but I can find out. It is free, I think.

                  B

                  • 6. Re: Weird and unwanted color gradient after Photomerge
                    gretchen_21 Level 1

                    @Berit: No, don't know the National Gallery stuff (how they do it), but it might be worth to figure out. Also what I see as an option: Maybe there are other programs around, that could import layered psd files but do a better seemless rendering. I tried Gimp, but it can't do it. Unfortunately, there's not much competition for Photoshop. And the really big boys, that do stitching of arial or satellite images (Google Earth), they might use some specialized software that would not be available to us... Cheers, g

                    • 7. Re: Weird and unwanted color gradient after Photomerge
                      PECourtejoie Adobe Community Professional

                      Hello, If the blending is ok, I would correct the first one with adjustment layers, and masks.

                      You might even try with a "correctly colored" patch, to use the "edit>adjustments>match color" function.

                       

                      It seems that the difference in colors is due to the differences in depth, and you get the equivalent of "underwater sfumatto" (atmospheric tinting)

                      • 8. Re: Weird and unwanted color gradient after Photomerge
                        gretchen_21 Level 1

                        Hi PE, I tried that, correcting one patch manually (which worked), but Match Color does not fix the others nicely. So maybe the manual way, patch by patch, is the way to go for now.

                         

                        Or just investing more time in preparing the individual stlls before using them, however, I find it very hard to get rid of any gradient caused by uneven lighting or the tinting effect. It works to some extend by applying tone correction via adjustment layers thru a gradient mask, but I do not get our stills perfectly even from corner to corner, but to be honest, the rendering engine of Photoshop should be able to deal with it. Incase you have ideas of how I could try to harmonize the initial stills, go ahead. My knowledge of PS is not too bad, but I'm not really familiar with pixel theory (histograms, curves and such). There might be some potential there. I might post an example image later, for people to play with. I do not have any high end experience, as with fine tuning pictures for print or such. Just hands on

                         

                        As it seems, this weird gradient has been accepted as a bug by Adobe, so hopefully they will fix it in a future release.

                         

                        Thanks for your thougths,

                        g

                        • 9. Re: Weird and unwanted color gradient after Photomerge
                          Berit Møller Level 1

                          Hi Gretchen

                          I have found the link to the app I was telling you about. Try it out and se if it works for you. It is designed for larges files.

                          http://www.vips.ecs.soton.ac.uk/

                          Berit

                          • 10. Re: Weird and unwanted color gradient after Photomerge
                            PECourtejoie Adobe Community Professional

                            Could you try to set up an action with Match color, and apply it to the stack?
                            When I say to blend the first one, I meant the first merged image you shown us. To correct the blended images in color and tone in one pass.

                            • 11. Re: Weird and unwanted color gradient after Photomerge
                              PECourtejoie Adobe Community Professional

                              In fact, I'm surprised that there would be enough pertinent information to be able to patch pictures of sand without any more detail or elements.

                              • 12. Re: Weird and unwanted color gradient after Photomerge
                                gretchen_21 Level 1

                                I use Match Color a lot during prep of the individual stills. However, it has limits to what extend it can remove color and brightness gradients in the images (caused by uneven lighting, as said)...

                                • 13. Re: Weird and unwanted color gradient after Photomerge
                                  gretchen_21 Level 1

                                  That's why I still love to use Photomerge. I do not let it do any attempts to auto-align images, though. I load them all in the top tray only, then grab them one by one. We shoot with 50% overlap, along a line and between the lines (we fly those lines with an underwater robot). And there's always patterns in the sediment, shells or stones that help me to find the overlap. Pure sediment of course is just the rim around the real object of interest, which normally are shipwrecks. Ther you got lot more structures for matching. Of course all images are numbered, so I always know the neighbours of a specific one. Additionally I plot the positions of the images in ArcGIS, so I would also spot gaps. Auto-aligning will not work, as long as a software would be smart enough to ignore the (moving) fishes and just to focus on the (still) pieces of wood or such. Cheers,

                                  g

                                  • 14. Re: Weird and unwanted color gradient after Photomerge
                                    gretchen_21 Level 1

                                    Thanks. This indeed looks very tekkie, I will need some time for this. Coding is not what I would call my mother tongue....

                                    g

                                    • 15. Re: Weird and unwanted color gradient after Photomerge
                                      TLL... Level 3

                                      This a very interesting thread with excellent documentation (the variety of things people us PS for is amazing eh?) Nice work!

                                       

                                      I work with aerial orthophotography, another notoriously uneven exposure environment. Much of what we see with uneven color/density issues are delt with after various imaging softwares do their 'auto' thing. We do a lot maual selecting and gradiant-like color adjustments. If everything else in your mosaics look good (seams, blending etc) why not apply a few colored gradiant masks to you images. I'd think that the right combination of color and transparency might bring your images up to a satisfactory level. Keeping in mind that all this image quality stuff can get very subjective, I'm still amazed at what we can do!

                                      • 16. Re: Weird and unwanted color gradient after Photomerge
                                        gretchen_21 Level 1

                                        H there,

                                         

                                        @TLL: you're right with what you said about the subjective element. Getting spoiled is easy, but staying ambitious is good as well. I do these mosaics since 2003, when Photomerge was part of Elements only. Then, in the first years with CS and CS2, I never had this bug with the color gradient being applied to the final merge. This started with, I guess, CS3 and I think it's due to enhancements Adobe made to the programm (making it more "intelligent"). Unfortunately, sometimes enhancements have dark sides and cause unexpected issues elsewhere. And since we are a minority (making large merges), these do not get fixed, since the majority, stitching what, 20 image panoramas of their home and garden do not suffer. Their images have strong contours and contrasts and the issue gets effective only on uniform images like underwater sediment or, in your case, landscapes shot from above. Going back to CS or CS2 is no option, since only the newer versions give me the processing power I need, also is the blending much smoother.

                                         

                                        I played around with gradient masks but I haven't got the right touch yet. Even if I get rid of the color differences, there will always be a brightness gradient, since borders of the images are always darker. And then, the weird gradient is a bright / dark one, not a red / yellow one. Not much better. Also, each batch job has to work for thousands of images, so has to be a compromise. I just cannot spend more than a day for a 1000 image mosaic, or a week for 6000 images, time is money on a ship (and elsewhere).

                                         

                                        I just think the solution would be, splitting the "Seemless tones and colors" function up into "Seemless Blending" (doing soft blending but not changing the colors) and "Seemless Color Transitions" (just dealing with the colors). And making both optional by check boxes...

                                         

                                        So far,

                                        g

                                        • 17. Re: Weird and unwanted color gradient after Photomerge
                                          gretchen_21 Level 1

                                          @TLL: So you are using photomerge as well for your work? In what context? I tried to find "pro" Software for arial stitching, that guys like Google use, but these programms (I guess, I don't know them), are often Linux and command line based, operated by programmers, which I'm not. VIPS, what Berit linked, could be one of these, but a bit over my head... Do you know one?

                                           

                                          g

                                          • 18. Re: Weird and unwanted color gradient after Photomerge
                                            TLL... Level 3

                                            Hello 'g'

                                             

                                            Since orthophoto imagery is georeferenced (to mapping coordinants, DTM, DEM and the like), mosaicing is done using a variety of geospatial applications. But for those instances where this type of accuracy is not needed/wanted, I make image mosaics using Photoshop and my workflow runs along the lines I described in this thread. So, no I don't use photomerge but I do use edit/auto blend. The other stitching software mentioned in that thread might be worth looking at too, but I'm getting too old (and invested in PS) to mess with to much new stuff. One other suggestion for the color issue - try painting with a monster brush in 'color' mode. You can get some pretty subtle effects that way too, but it doesn't fix the density shifts. Altho I think you might be a bit hard on yourself expecting that expanse of image area (under water no less) to maintain an even appearance. I wouldn't think that would even be true in nature. You perfectionists

                                            • 19. Re: Weird and unwanted color gradient after Photomerge
                                              gretchen_21 Level 1

                                              This would be a good example by the way. The first one shows, how the images come off the camera. Does not look too bad on first sight, but a basic level correction reveals the differences between top and bottom and corner to center. Optimizing the lighting is pretty difficult on an ROV (dive robot). I do more than just levels, yes, like "Match Color" (to harmonize the thousands of images), some "Replace Color" (to turn the reddish into greenbrownish, and some lighting up the corners. But there's always some residuals, that cause the Photomerge rendering or the "Auto Blend Layers" function to screw it up in the described way (applying the found gradient to the overall merge).

                                               

                                              Any ideas welcome,

                                              g

                                               

                                              A.jpg

                                              B.jpg

                                              • 20. Re: Weird and unwanted color gradient after Photomerge
                                                PECourtejoie Adobe Community Professional

                                                Hello again. If he issue is uneven lighting, look at this technique involving high pass to even out patterns: http://www.gamasutra.com/view/feature/131482/the_power_of_the_high_pass_filter.php?print=1

                                                • 21. Re: Weird and unwanted color gradient after Photomerge
                                                  gretchen_21 Level 1

                                                  Wow, thanks, that definitely looks promising. His "Wall" shot after the treatment is what I want, I will test it for sure. Thanks again,

                                                  g

                                                  • 22. Re: Weird and unwanted color gradient after Photomerge
                                                    gretchen_21 Level 1

                                                    Courtejoie, I owe you big time, that was the best tipp ever, it's exactly what I needed. Or the pictures. Many, many thanks, the results are almost seemless now, no weird color gradient or anything, I'm happy! Post could be closed, however, it was a pleasure, thanks to everyone contributing!!

                                                     

                                                    g